The present invention relates to method for producing a magnetic recording medium, and more particularly relates to improvements in production of a magnetic recording medium such as a magnetic disk by a process including formation of an anodic oxide layer on an Al or Al-base alloy substrate and precipitation via electrolysis of magnetic substance in pores formed in the anodic oxide layer.
Production of a magnetic recording medium by the above-described process is well known from, for example, Japanese Patent Publication No. Sho. 51-21562 and its products are widely accepted as well suited for use in perpendicular magnetic recording system. In the above-described process, the substrate as an electrode is twice subjected to electrolysis and, for this reason, power has to be supplied to the substrate.
To this end, use of an aluminium lead is conventionally employed in general in connection with a doughnut shaped substrate. More specifically, a thin, high purity aluminium lead is attached to the inner or outer periphery of a substrate by welding. A number of substrates are arranged side by side in an electrolytic bath with their aluminium leads being connected to a common power source so as to act as one electrode during electrolysis. The other electrode is formed by counter plates arranged in the electrolytic bath spacedly facing the group of substrates. The electrolytic bath contains oxalic acid or sulfuric acid soultion.
Despite merits derived from use of the aluminium leads, this power supply system is inevitably accompanied by several drawbacks. In order to obtain a uniform covering layer on each substrate, a large distance should be left between the group of substrates and the counter plates thereby inevitably enlarging the size of the electrolytic bath. Such an enlarged size of the electrolytic bath causes increased installation cost and large consumption of the electrolyte. Difficulty in attachment of the aluminium leands and their reliable insulation makes the process quite unsuited for mass-production. After detachment of the aluminium lead, the substrates have to be subjected to removal of welding scars. In addition, when the aluminium lead is attached to the inner periphery of the substrate, a shade in treatment may be left of the covering layer near the spot of the attachment since presence of the aluminium lead tends to bar smooth formation of the covering layer.
With the above-described process, further, the surface of the product, i.e. the magnetic recording material is totally covered by an insulating alumite layer. When electrostatic accumulation occurs on the magnetic recording medium during its usage, total presence of such an insulating alumite layer hinders smooth discharge of electrostatic accumulation since there is no possibility of grounding. Such electrostatic accumulation often causes generation of harsh noises at pick-up by a magnetic head. Generation of such noises is in particular significant and serious when the magnetic recording medium is driven for rotation in a relatively dry environment.